An electronic vision system includes an image pickup mechanism and an image-processing unit. The image pickup mechanism includes a pickup camera and a lighting apparatus. The image-processing unit includes an image processor, a television coder, and an image display unit.
The image pickup element of the pickup camera includes a photo-sensor. The photo-sensor currently used mostly involve a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) device.
It is the principle generating light of the fluorescent lamp of the lighting apparatus that a fluorescent light is excited on when electrons emitted from two electrode terminals impact fluorescent substances on the inside surface of the lamp in the electrified state. For lighting with the fluorescent lamp, it is necessary to solve the flicker problem. The illumination intensity of the fluorescent lamp changes with the waveform of the AC power source and has a frequency equal to that (such as 60 Hz) of the AC power source. Though it is not easy for eyes of men to detect the flicker of the fluorescent lamp due to persistence of vision, the CCD of the pickup camera cannot pick up correct images under the circumstances of this light source.
It is the main objective of the image processor that the processor receives visual information transmitted from the CCD of the pickup camera, converts the information into digital image data for storing into an image storage unit, and can perform image processing and analyzing. As the image processor must fit with the CCD of the pickup camera, the specification of the used image signal between the image processor and the pickup camera must also agree. Two kinds of the common color visual information standards are NTSC and PAL.
The television coder converts the digital image signal output from the image processor into an analogue compound signal or an analogue television signal with both brightness and color difference being separate for providing to the television set or the image display unit to display.
The pixel field frequency of the NTSC monitoring system is 59.94 fields/sec, and the flicker frequency of the fluorescent lamp is generally also 60 Hz in the state the power frequency being 60 Hz. Not considering the correlation between the two frequencies, under the circumstances of the fluorescent lamp, as the integral value of the light amount in each pixel field is different, the photo sensing state of the CCD sensor in the each pixel field can be different from that of another, which makes the photo sensing distributions be not even among the pixel fields. Therefore, the phenomenon known as the color rolling occurs; that is, the image will vary periodically, which makes one unable to accept. The current general solutions all have that additional devices are appended to an external circuit, which dynamically adjusts an external clock frequency, for providing the frequency to the image processor to use. In this way, not only increases the cost but it is not easy to exactly adjust the external devices.
A prior art solving the phenomenon of the color rolling is disclosed in the US Publication No. 2005/0253941. In this prior art, main color signals are extracted from an image signal received. Integral data of each color signal are calculated according to the main color signals extracted. Whether the phenomenon of the color rolling begins to occur is determined according to the variation of the integral data of the each color signal. When the phenomenon of the color rolling is detected, a high-speed white balance is used for suppressing the phenomenon.
Another prior art solving the phenomenon of the color rolling is disclosed in the US Publication No. 2005/0200704. In this prior art, a solid-state image pickup device produces an image pickup signal. A light amount detector detects a light amount injecting into the solid-state image pickup device. A correction circuit receiving the light amount detects periodical variations of the light amount, and corrects the image pickup signal according to the periodical variations.
The two above prior arts both includes steps of detecting the incident light of the light source, obtaining the color variation through analyzing, and correcting the image signal picked up for suppressing the phenomenon of the color rolling. In this way, the complexity and the whole cost of the image processing will be increased.
In sum, how to suppress the phenomenon of the color rolling with a simpler circuit and a lower cost becomes the primary motive of the present invention.